Manufacture of snap-acting devices



March 10, 1964 c. D. FLANAGAN 3,123,903

MANUFACTURE OF SNAP-ACTING DEVICES Filed Aug. 23, 1961 5 Sheets-Sheet 1 FIG. I.

March 10, 1964 c. D. FLANAGAN 3,123,903

' MANUFACTURE OF SNAP-ACTING DEVICES Filed Aug. 23, 1961 5 Sheets-Sheet 2 FIG] 71 March 10, 1964 c. D. FLANAGAN MANUFACTURE OF SNAP-ACTING DEVICES 5 Sheets-Sheet 3 Filed Aug. 23, 1961 FIG.4.

March 10, 1964 c. D. FLANAGAN 3,123,903

MANUFACTURE OF SNAP-ACTING DEVICES Filed Aug. 23, 1961 5 Sheets-Sheet 4 FIG. 5.

March 10, 1964 c. D. FLANAGAN MANUFACTURE OF SNAP-ACTING DEVICES 5 Sheets-Sheet 5 Filed Aug. 23, 1961 FIG. 6.

United States Patent 3,123,903 MANUFACTURE OF SNAP-ACTING DEVICES Charles D. Flanagan, Attleboro, Mass., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Aug. 23, 1961,, Ser. No. 133,506 23 Claims. (11. 29-407 This invention relates to the manufacture of snap-acting devices, and with regard to certain more specific features, to their formation, stabilization and testing.

Among the several objects of the invention may be noted the provision of a rapid, low-cost method of and apparatus for accurately forming, stabilizing and testing snap-acting devices such as, for example, monometallic, composite, or bimetallic snap-acting plates of various forms, including discs; the provision of a method and apparatus of the class described according to which rapid formation, stabilization and testing may be carried out under a variety of parameters at a single station in a single device; and the provision of a method and apparatus of this class adaptable for the manufacture of snap-acting devices of various shapes, both regular and irregular and whether perforated or unperforated. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, steps and sequence of steps, features of construction and manipulation, and arrangements of parts which will be exemplified in the constructions and methods hereinafter described, and the scope of which will be indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a diagrammatic view, partly in section, illustrating one form of the invention for the manufacture of unperforated devices;

FIG. 2 is an enlarged cross section taken on line 22 of FIG. 1;

FIG. 3 is a diagrammatic cross section of a directional control valve used with the form of the invention shown in FIGS. 1 and 2;

FIG. 4 is a front elevation of a second embodiment of the invention for both perforated and unperforated devices, parts being broken away;

FIG. 5 is a left-side elevation of FIG. 4, parts being broken away;

FIG. 6 is an enlarged fragmentary view, similar to FIG. 5, parts being broken away; and

FIG. 7 is a cross section taken on line 7-7 of FIG. 6.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

While the invention has primary application to the manufacture of thermotropic devices, such as snap-acting bimetallic discs, and will be described in relation thereto, it will be understood that its applications are broader and that it may be used to manufacture any plate-like device requiring deformation for example a so called non-developable deformed portion to bring about a de sired condition for snap action. Thus the manufacture of monometallic snap-acting spring devices is contemplated herein, as well as composite and bimetallic thermotropic devices.

Snap-acting thermotropic devices for the manufacture of thermostats and the like are generally formed of composite bonded sheets (often bimetallic sheets). These, like the spring devices above mentioned, are required to be deformed in one manner or another in order to set up conditions for stresses therein which are responsible for their snap actions. In the case of thermotropic devices, snap action occurs in response to temperature changes. The shape and degree of the deformation determine the snap action characteristics and in the case of a thermotropic device determines the temperature of operation. The usual manner in which the shape is determined is by forming the device between dies such that at least one die is shaped completely to determine the form of the device. This requires a relatively large number of different dies which are costly to make, particularly when a variety of shapes of the devices are contemplated.

Moreover, snap-acting devices, in general, after their formation have required thermal aging steps to effect stress relief for stabilization of the snap action characteristics of the deformed device. Heretofore such stabilization required removal from the forming die for the performance of the stabilization step in a separate apparatus. By means of the present invention cumbersome and time consuming thermal aging stabilization steps are advantageously replaced by a mechanical cycling stabilization which can quickly and economically be performed in the same apparatus without necessitating removal of the disc from the apparatus.

After snap-acting thermotropic devices have been stabilizing, they are required to be tested for operation at the desired temperature, and this operation again requires additional apparatus for the purpose. Heretofore this has involved a costly procedure including applications of proper different temperatures to the devices to be tested. By means of the present invention, the forming, mechanical stabilizing and mechanical testing operations can be rapidly carried out at low cost in a single piece of apparatus, wherein intricate die shapes are not required, nor applications of varying temperatures.

While composite thermotropic plates and other spring devices take many forms, such as rectangles, elliptical shapes, discs with and without ears, etc., the present invention for the purpose of example will be described in connection with the formation, stabilization and testing of round discs of the bimetallic variety, and to avoid circumlocution in the appended claims, the term plate will be understood to comprehend any plate-like device in connection with which the invention is useful.

Briefly, the present invention comprises locating a substantially flat or partially preformed plate in a clamp, properly locating its peripheral margin, and applying pressure to one or both sides to effect deformation, then applying pressure alternately to its opposite sides to stabilize its operation, and then checking its snap-acting operating characteristics by raising the pressure in the appropriate chamber and noting the pressure or force value at which the disc snaps. For thermotropic devices the present invention advantageously permits a close correlation between forming pressures and temperature operation of the device at which snap action will occur to more predictably provide for greater yields. Further the invention affords a direct correlation between test pressure and snapping temperature for accurately ascertaining the temperature operational characteristics of the device without actually subjecting the device to various different temperature conditions as heretofore required. In one form of the invention, pressure application is effected by hydraulic means, and in another form by mechanical means. In both forms the plate or disc does not require transfer from one machine to another in order to effect the three forming, stabilizing and testing operations. Thus manufacture is simplified, whether or not operations are manually controlled or automated. Moreover, automation can more readily be accomplished because all operations are rapidly performed in a single device at a single station.

Referring now more particularly to FIGS. 1-3 of the drawings, which show a hydraulic form of the invention, there is shown at numeral 1 a supporting framework for a pair of holders 3 and 5 for positioning a narrow margin of a preferably, but not necessarily, flat bimetallic disc 7. The holders 3 and 5 when together form a fluid chamber means divided by the disc into two compartments 9 and 11. The holders 3 and 5 have opposing faces adapted for sealed engagement. The face of holder 3 contains a circular recess in which is an O-ring 13 for sealing purposes. Holder 3 also has holes 15 for the reception and guidance of pins 17. These extend from the engaging face of holder 5. The inner margin of each holder 3 and 5 is preferably provided with a narrow ledge-forming recess 19 to form a support for the narrow margin of the disc 7. The depth of each recess is preferably greater than one-half the thickness of the disc to avoid vertical restraint (as seen in FIG. 1) of the disc 7. If desired, only one ledge-forming recess may be employed on the lower holder 3 which is greater than the thickness of the disc. The ledge forming recess 19 provides for proper location of the disc '7 and cooperates therewith to provide an adequate seal between the compartments while avoiding restraint to the marginal peripheral portion of the disc to permit the latter to flex fairly freely. Bevel portions 2 and 4, extending toward the recess means for the disc, provide clearance of free fiexure of the disc and ensure adequate sealing during the forming or cycling operations.

Holder 5 is upwardly retractable from holder 3. This is accomplished, for example, by a forked connection 21 with a piston rod 23 which may be driven up and down by means of a piston 25 in a cylinder 27. Fluid control means 23 may be employed for operating piston 25. Numerals 3 1 and 33 indicate adjustable stops threaded into the holders 5 and 3, respectively, and extending into the compartments 9' and 11, as shown. These preferably have fiat ends although it should be understood curvilinear or other shapes may be employed where desired or required. O-ring seals are shown at 39 and 41 to seal the stops 31 and 33 against leakage from the compartments 9 and 11. The amount of the projection of the fiat end of each stop into the compartments is effected by turning it from a knob 35 or 37 as the case may be. The adjustable stops 31 and 33 permit the forming of a wide variety of different shapes and discs of varying snapacting characteristics, thereby eliminating the necessity for many different dies for a given dimension or diameter of disc.

Compartments 9 and 11 are provided with ports 43 and 45, communicating with pipes 47 and 49, respectively, the pipe 47 having a flexible section 51 to accommodate vertical movement of the holder 5. The pipes 47 and 4-9 lead through a directional valve 53 such as illustrated in FIG. 3. This valve has spaced inlet ports 55 and 57, having a branched connection 59 with a supply pipe 61 in which is an adjustable pressure-reducing and cutoff valve 63. Pipe 61 forms the outlet from a hydraulic pump 65 having a suction line 67 leading from a sump 6?. At numeral 71 is a return line to the sump 69. The valve 53 has an exhaust line 73 connecting with the return line 71. A catch basin 75 is connected with said line 71. Lines 47 and 49 include pressure gages 48 and 5t), respectively.

The directional valve 53 may have its control spool 54 set from a handle 56 into either of two alternate positions. In the position shown in FIG. 3, pressure may be supplied to compartment 9 over line 47, the amount of pressure being readable at gage 43. Pressure is at this time released from compartment 11 through line 49 and exhausts 73 to the sump 69.

Conversely, the spool 54 of valve 53 may be set into an alternative position to that shown in FIG. 3. In this event, pressure is supplied to compartment 11 and released from compartment 9. The pressure supplied to compartment 11 is readable at gage 50.

The pump 65 has a conventional by-pass return connection to the sump 69. Numeral 70 indicates a constant pressure value in the by-pass connection 68 for maintaining constant back pressure on the pump outlet. The amount of pressure supplied to the directional valve 53 is determined by the reducing valve 63 and its value may be read at either gage 48 or 50, depending upon how the valve 53 is set. When valve 63 is set at its off position, no pressure is delivered to the directional valve 53.

Operation is as follows, assuming the pump 65 to be supplying pressure constantly and the valve 63 closed:

By suitable controls in line 29, the piston 25 may be raised to retract holder 5 from holder 3. This separates compartment 9 from compartment 11, so that a bimetallic disc 7 (for example) may be placed on the ledge 19 of compartment 11 to properly locate the disc 7. Then the holder 5 is forced down with sufficient force to ensure adequate sealing of compartments 9 and 11. Assuming that the disc is to be deformed in a downward direction as seen in FIG. 1, the stop 33 may be adjusted if desired to limit the amount of deformation at its center. It will be understood that in some cases stop 33 will be placed so as to remain out of engagement with disc 7 during the forming operation. Valve 63 is then set to admit a predetermined pressure to compartment 9. This deforms and presses the center of the disc against stop 33 if it is positioned for engagement with the disc. The deformation at the center of the disc is of the amount desired, according to the setting of the stop. Pressure is applied (the amount of which is determinable at gage 48) and the portion of the adjustable stop provide the parameters to obtain the desired shape for snap action of the disc at a predetermined temperature. It should be noted that this first forming operation under equal unit pressures over the area of the disc differs from that obtained in the usual manner by a die having the shape desired for the disc. Thus in the present case, after the center of disc touches stop 33, annular portions of the disc around the stop may if desired be further deformed by increase in pressure above that which would be required only to bulge the center of the disc against the stop.

It should be noted that a reverse forming step may also be carried out by relieving the pressure on compartment 9, properly adjusting stop 31 in compartment 9 and by applying the required pressure in compartment 11 (determinable at gage 50) The second operation is that of stabilization and consists of reversely cycling the disc several times from one curvature to a reverse curvature by applying pressure alternately to the opposite sides of the disc. This is done by alternately changing the position of the directional valve 53, which releases pressure from one side of the disc upon application of pressure to its opposite side. Preliminary to this cycling operation, the stops 31 and 33 are preferably retracted to avoid engagement with the disc or the stops may be left in place and sufiiciently low cycling pressures may be employed to avoid engagement between the disc and the stops. This second cycling operation stabilizes the stresses in the disc. The pressure employed for cycling need not equal that required for the first forming step.

The third operation is a checking operation to determine the pressure at which the disc will snap which is accomplished by retracting stops 31 and 33 to avoid engagement with the disc and by slowly raising the pressure in the compartment 11 and noting the value on gage 50 at which the disc snaps to its upward curvature. With so-called automatic type discs, pressure is gradually released in compartment 11 until the disc 7 snaps back, the pressure on snapping back being noted on gage 50. With manual type discs (i.e., those which have two positions of relative stability generally of opposite concavity as in the case of a disc with a nondevelopable portion responsible for its snap action) after such snap action, pressure may be gradually built up in the chamber 9 and the value noted on gage 48 at which the disc snaps back, pressure having been at this time released from compartment 11. It has been found that in the case of thermotropic devices there is a correlation between the pressure at which the disc will mechanically snap at a given ambient temperature and the temperature at which it will snap. Accordingly, the pressure-checking operation is also a temperature-checking operation for thermotropic devices.

The above description of operation has been made on the assumption the disc is to be bulged or deformed downwardly (as seen in FIG. 1). If it is to be bulged upwardly, the pressure for deforming is admitted to compartment 11, stop 31 being appropriately set. The operations for stabilization and checking under these circumstances will be obvious from the above. After forming, stabilization and testing or checking have been completed, valve 63 is closed and the holder 5 retracted from holder 3 to expose the finished disc for removal. The pan 75 is for the purpose of catching any spilled fluid during this event.

Even under conditions of manual operation, the invention thus far described has advantages in that all of the forming, stabilization and testing are quickly and economically accomplished in a single device at a single location. The forms of the holders 3 and 5 are simple in comparison with the usually more complex dies that are employed in die-forming operations. Once formed, each die, as formerly employed, is useful for plates of only one curvature. By the employment of the above-described stops such as 31 and 33 there will be accommodated the manufacture of discs of various curvatures.

To ensure desired and predictable operating temperature characteristics in formed thermotropic discs, it is preferred that the forming, stabilizing and checking steps be carried out under controlled steady ambient temperature conditions.

It has not been possible heretofore to stabilize plates in their locations in the formerly used dies. Also, calibration heretofore had to be carried out by subjecting plates to temperature variations, whereas by means of the present invention the correlation between temperature and pressure operation is advantageously utilized for checking purposes. Another advantage of the invention is that if a particular plate after treatment indicates under check that it has not been correctly formed or that the stabilization has varied its characteristics, it may be again subjected to the forming operation to correct conditions. Also, if it is desired to automate the procedure of forming, stabilization and testing, this can readily be accomplished by timing these events through suitable automatic controls for the various valve settings.

It should be understood that, while my invention has thus far been described as utilizing a liquid to create the required pressures, a suitable gas system may also be employed to provide the required pressures.

Another advantage of the FIG. 1-3 embodiment over many prior methods is that forming of the discs is accomplished without the creation of surface blemishes which can adversely affect the cyclic operational life of the disc.

In FIGS. 47 is shown another form of the invention useful for plates such as that described above for the FIGS. l-3 embodiment as well as for perforated plates or other types of plates which are not self sealing as required for the FIG. 1-3 embodiment. In this case, numeral 11 indicates a frame on which are mounted rigid supports 79 for fixed vertical guides 81. Guides 81 carry upper and lower sliding crossheads 83 and 85. Frame 77 also carries a bracket 87 which supports a platen 89. This platen supports a lower fixed disc holder 91 in which is a pocket 93 having a ledge-forming recess 95 for supporting the peripheral margin of a disc 97. Disc 97 may or may not be perforated. A perforated disc is shown for example. Above the fixed holder 91 is a movable holder 99 having downwardly extending guide pins 101, slidable in guide openings 103 in the platen 89. This holder also has a pocket for placement adjacent recess 95. Springs 105 in recesses in the holders 91 and 99 and surrounding the pins 101 bias the upper holder 99 upward from the closed position shown to an open position. FIG. 6 shows a closed position and FIGS. 4 and 5 show partially open positions. Extending downward from the movable holder 99 are two pins 107 which extend through openings in the holder 91 and the platen 89 to points below the latter. Here these pins are notched, as shown at 109, for the reception of a pair of wedges 111 in the form of a fork 113. The fork has an operating rod 115 passing through a bearing 117. The outer end of the rod 115 has a slot and pin connection 119 with a lever 121, pivoted at 123. By swinging the lever 121 in one direction, the wedges 111 may be moved to force down the pins 107. The lever can also be swung in the reverse direction to allow springs 105 to push open the upper holder 99. When open, a disc may be inserted into or removed from the holders 91 and 99.

Above the crosshead 83 is a drive therefor. This consists of brackets 125 and 127, carrying bearings 129 and 131 for sprocket 133 and a hub 135. The latter is formed with a nut 137 threaded on a screw 139 which at a connection 141 is rigidly attached to the crosshead 83. A chain drive 143 from an upper reversing motor 145 is provided for rotating the sprocket 133 and the nut 137 which it drives. The position of the motor is transversely adjustable through a bolt and slot connection 147 with a bracket 149 on the frame 77.

A lower bracket 151 supports a lower reversing motor 153, having a bolt and slot connection 155. A chain drive 157 connects motor 153 with a sprocket 159, carried on a bearing 161 in bracket 163 on frame 77. The sprocket 159 has a hub 165, formed in part as a nut 167 threaded on a screw 169 affixed at 171 to the lower crosshead 85.

In View of the above, it will be seen that by properly exciting the reversing motors 145 and 153, the crossheads 83 and 85 may independently be driven up and down.

At numerals 173 and 175 are shown force transducers which are alike in form, so that the description of one of them (namely, transducer 173) will be suificient for both, like numerals designating like parts in each. However, the position of each transducer is inverted with respect to the other.

Each transducer consists of a spring ring 177 carrying screw attachments 179 and 181. One attachment 179 fastens the upper ring 177 to the upper crosshead 83, and the other attachment 181 fastens it to an upper plunger 183, a nickel threaded head 185 being employed for the purpose. The other ring 177 also has an attachment 181 with a lower plunger 187, this being effected through a nipple 189. Another attachment 179 fastens this other ring 177 to the lower crosshead 83. Plunger 183 extends through an upper opening in the upper holder 99. Plunger 187 extends through a lower opening in the lower holder 91. Each ring 177 supports within one side of it a housing 191 of a differential transformer 193. The housing 191 in turn supports the differential transformer windings, one of which is an energizing winding indicated at 195, and the other of which comprises a split signal or output winding having two portions or segments 197a and 197k.

Extending from the opposite side of each ring 177 is a plunger 199 which carries a magnetic armature 201. If force is applied to either ring 177 along the axis of its plunger 199, the ring will be squeezed from a circular to an oval shape, thus changing the position of the armature 201 with respect to the split signal output coils 197a and 19712. The result is a change in the electrical coupling between the energizing winding 195 and the two circuits containing windings 197a and 1971;. It will be 7 clear that by measuring the differential output from windings 197a and 1971) (which will vary in relation to the position of armature 261) the forces applied to plunger 19? can readily be determined. Thus the value of a force applied to either ring 177 may be translated into an electrical value readable on the dial of a suitable instrument in a suitable circuit (not shown), which may also include means for controlling the amount of force applied to the plungers. The dotted line configuration of the upper ring 177 illustrates its undefiected form, while "the solid lines illustrate a deflected configuration such as caused by applied pressure. While the differential transformer is of a desirable type used in force transducers for registering ring deflections, and a proving ring type transducer has been shown and described it is to be noted that other indicating means known in the art may be used for the purpose of giving information as to as well as controlling the force applied to the plungers 195 Operation of this form of the invention is as follows:

By operation of the handle 1Z1, wedges 111 may be retracted, allowing the upper holder 99 to be opened by springs 19S. Thereupon a disc (preferably substantially flat) may be inserted between the holders. Holder 99 is then reclosed by moving handle 121 to advance the wedges 111 to their closing positions. Next the upper motor 145 is operated for a predetermined time to drive down the upper plunger 183 into engagement with the upper side of the disc, and to force its bottom side a certain distance toward the upper end of the plunger 187. The latter may or may not act as a stop. There may be situations in which, in order to obtain specific operating characteristics, it is necessary to position plunger 187 such that its upper end will be spaced from the lower side of the disc an appropriate amount to limit downward deflection therein. Then when upper motor 145 is operated to drive down the upper plunger 183 into engagement with the upper side of the disc, the deformation is limited by the upper face of plunger 187, acting as a stop. This condition is illustrated in FIG. 6, wherein the deformed disc is numbered 97.

The reactive force required for bulging or deforming the disc 97 downwardly (as seen in FIG. 6) will result in distortion of the upper spring ring 177, for example, from the dotted-line position to the solid-line position shown. This drives down the split coils 197a and 17b as well as coil 195 relative to the armature 291 of the upper transducer 173. As a consequence, the force required can be read off electrically or otherwise, as above suggested.

If the disc touches the lower plunger 187, a signal will also appear in the electrical apparatus connected with the lower transducer 175. This signal is a sign that the disc has been deformed the required amount and the electrical reading in connection with the upper transducer 173 is an indication of what force was used to accomplish such deformation. By this means the parameters of deflection and force required therefor may be repeated throughout a production run of the discs.

After a disc has been formed, it may be stabilized immediately by operating the motors 145 and 153 so as to mechanically flex it back and forth a number of times. Finally, each disc before removal from the holders 99 and 91 may be tested to determine whether the disc will operate at the desired temperature by, for example, retracting the plunger 133 when the disc is bowed downward and slowly raising the plunger 187. Deflection will then occur in the spring ring 177 of the lower transducer 175. The amount of force required to snap the disc upward will be indicated by the signal obtained from the lower force transducer 175. Conversely, when the disc is bowed upward, the lower plunger 187 may be retracted and the upper plunger 183 driven down to snap the disc back to its original position, the amount of force being obtained by signal from the upper transducer 173. As a correlation has been found to exist between the force required for snapping and the temperature required for snapping, the operator has a convenient means to determine the snapping temperature.

In view of the above, it will be seen that the second form of the invention, like the first form, permits of forming, stabilizing and testing a disc in a single holder at a single station, the advantages of which have been discussed above. The second form of the invention differs from the first in that mechanical instead of fluid means are employed for applying pressure to the disc for forming, stabilizing and testing it.

While the invention has been described in reference to the manufacture of round, disc-shaped plates, it will be understood that it is also applicable to the manufacture of other shapes and plans simply by forming the marginal supports for the discs in the holders such as 3, 5 or 91, 99 properly to hold the disc margins. It will of course be apparent that the form of the invention shown in FIGS. 4-7 is applicable to perforated plates or discs. Further, the present invention is advantageously particularly applicable to blanks (either flat or preformed) which have contacts or other parts, e.g., welding projections, rivets, adjusting mounting screws, etc. attached thereto prior to forming.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of manufacturing a snapacting plate comprising holding its margin, positioning a stop in spaced relation to one side of the plate for engagement thereby throughout an area of contact substantially less than all of its area, pressing the other side of the plate to deform it 'into engagement with said top, and thereafter while continuing to hold its margin supplying pressure to the side of the plate on which said stop is located to deflect the plate from its deformed configuration.

2. The method according to claim 1, including the step of testing the plate for snapping characteristics by gradually increasing pressure on either side until snap occurs.

3. The method according to claim 1, wherein said pressure steps are accomplished by applying a predetermined mechanical force.

4. The method according to claim 1, including the step of positioning a second stop on the other side of the plate adapted to limit said last-named deflection.

5. The method of forming a snap-acting plate comprising holding its margin, positioning stops in spaced relation to opposite sides of the plate for engagement thereby throughout areas of contact substantially less than all of its area, and alternately applying pressure to opposite sides of the plate while releasing pressure from opposed sides to deform it alternately between said stops, first deforming it in one direction to stress it for snap action and then reversely deforming it to attain desired operating characteristics.

6. The method according to claim 5, including the step of testing the plate for snap action at a predetermined temperature by gradually increasing pressure on either side until snap occurs.

7. The method according to claim 5, including the steps of alternately applying pressure to opposite sides of the plate while releasing pressure from opposed sides for stabilization of said stress, said plate remaining out of engagement with said stops during said stabilization steps.

8. The method of forming a snap-acting plate comprising holding its margin, positioning stops in spaced relation to opposite sides of the plate for engagement thereby throughout areas of contact substantially less than all of its area, alternately applying mechanical force to opposite sides of the plate while releasing force from opposed sides to deform it alternately between said stops, first deforming it in one direction to stress it for snap action and then reversely deforming it to attain desired operating characteristics, and alternately applying mechanical force to opposite sides of the plate while releasing force from opposed sides for stabilization of said stress, said plate remaining out of engagement with said stops during said stabilization steps.

9. The method of forming and testing a polymetallic thermally responsive plate, comprising holding its margin, positioning stops in spaced relation to opposite sides of the plate for engagement thereby throughout areas of contact substantially less than all of its area, alternately applying mechanical force to opposite sides of the plate while releasing force from opposed sides to deform it alternately between said stops, deforming it in one direction of stress for snap action and then reversely deforming it to attain desired operating characteristics, and finally testing the plate for snap action at a predetermined temperature by gradually increasing force on either side until snap occurs.

10. Apparatus for manufacturing a snap-acting plate comprising means adapted to hold marginal portions of the plate and to provide compartments on its opposite sides for accommodating plate movements, means in one of the compartments adapted to apply pressure to one side of the plate to deform it in one direction of curvature in one of said compartments to stress it for snap action, means in the other compartment adapted to apply pressure to the other side of the plate to snap it from said curvature into a reverse curvature in the other compartment to stabilize it, and means connected to said pressure applying means for testing the plate.

11. Apparatus for forming, stabilizing and testing a snap-acting plate comprising an openable and closable holder adapted to receive the plate and upon closing to hold it marginally and to provide fluid compartments on opposite sides of the plate, adjustable stop means in said compartments respectively, fluid pressure connections with said compartments, and means adapted alternately to apply hydraulic pressure to and release pressure from said compartments through said connections to form, stabilize and test the plate.

12. Apparatus for forming, stabilizing and testing a snap-acting plate according to claim 11, including pressure gages in said connections.

13. Apparatus for forming, stabilizing and testing a snap-acting plate comprising an openable and closable holder adapted to receive the plate and upon closing to hold it marginally to provide spaces on opposite sides of the plate, plungers extending into and movable within the spaces respectively, and means adapted independently forcibly to drive said plungers so that each may assume a position independently of the other and each may function as pressurizing means to deform and deflect the plate toward the other.

14. Apparatus for forming, stabilizing and testing a snap-acting plate according to claim 13, including a force transducer between each drive means and its plunger providing a deflection responsive to reactive force on the plungers from the plate.

15. Apparatus for forming, stabilizing and testing a snap-acting plate according to claim 14, wherein each force transducer is constituted by a deformable spring ring having parts relatively movable upon springing, one of said parts carrying the field windings of a differential transformer and the other carrying an armature movable relatively thereto and adapted to vary the coupling between the transformer windings in response to deflection of the spring ring.

16. The method of forming snap-acting devices from a plate of material having a predetermined peripheral form, comprising supporting at least a part of the periphery of the plate on a shelf-like support between two compartments in respect to which the plate forms a common wall, introducing sufficient fluid under pressure into one of said compartments while releasing pressure from the other to deform and stress the plate for snap action, alternately introducing fluid under pressure into each of said compartments while alternately releasing pressure from the other after the plate has been deformed to stabilize it by snap action, the last-named introductions of fluid being carried out under pressures less than that required to deform the plate, and thereafter checking conditions under which the plate will snap by introducing fluid into one or the other of said compartments under gradually rising pressure.

17. The method of forming snap-acting devices from a plate of material having a predetermined peripheral form, comprising supporting at least a part of the periphery of the plate on a shelf-like support, applying suflicient unbalanced pressure to one side of the plate to deform it for snap action, and then applying less unbalanced pressures alternately to opposite sides of the plate to stabilize it.

18. The method according to claim 17, including a final step of checking conditions under which the plate will snap by applying unbalanced pressure to one side or the other of the same under a gradually rising condition of pressure.

19. The method of forming snap-acting devices from a plate of material having a predetermined peripheral form, comprising supporting at least a part of the periphery of the plate on a marginal support between two fluid-tight compartments in respect to which the plate forms a common wall, locating first stop means in one of said compartments in spaced relation to a first face of the plate to function as a stop against bulging of the material, locating second stop means in the other of said compartments, introducing fluid under pressure into said other compartment to deform the plate against said first stop means to deform and stress it for snap action, and applying fluid pressure to said one compartment while releasing pressure from said other compartment to snap the deformed plate against said second stop means.

20. The method of forming snap-acting devices from a plate of material having a predetermined peripheral form comprising supporting at least a part of the periphery of the plate on a marginal support between two compartments in respect to which the plate forms a common wall, introducing suflicient fluid pressure into one of said compartments while releasing pressure from the other to deform and stress the plate for snap action, and introducing fluid under pressure alternately into said compartments while releasing pressure from the other after the plate has been deformed to stabilize it.

21. The method of forming a snap-acting bimetallic plate comprising holding its margin, positioning a first stop in spaced relation to one side of the plate for engagement thereby throughout an area of contact substantially less than all of its area, positioning a second stop on the other side of the plate, applying hydraulic pressure to said other side of the plate to deform it against said first stop to stress it for snap action, and applying hydraulic pressure to the first-named side of the plate while releasing pressure from the other side to deflect the plate against the second stop.

22. The method of forming a snap-acting device from a plate of material having a predetermined peripheral form, comprising supporting at least a part of the periphery of the plate on a support between two compartments in respect to which the plate forms a common wall, first deforming the plate in one direction into one compartment to stress it for snap action and then reversely deforming it into the other compartment to attain desired operating characteristics.

References Cited in the file of this patent UNITED STATES PATENTS Sivian et a1. June 2, 1942 Walton Apr. 27, 1943 Staubitz Mar. 27, 1956 Peters Sept. 4, 1956 FOREIGN PATENTS Great Britain Nov. 11, 1949 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 123,903 March 10, 1964 Charles D, Flanagan It is hereby certified that error appears in the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 4, line 32, for portion" read position column 5, line 68, for "'11" rea 77 column 8 line 40, for "top" read stop column 9 line 72, for "deflection" read deflections Signed and sealed this 7th day of July 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Commissioner of Patents Attesting Officer 

1. THE METHOD OF MANUFACTURING A SNAPACTING PLATE COMPRISING HOLDING ITS MARGIN, POSITIONING A STOP IN SPACED RELATION TO ONE SIDE OF THE PLATE FOR ENGAGEMENT THEREBY THROUGHOUT AN AREA OF CONTACT SUBSTANTIALLY LESS THAN ALL OF ITS AREA, PRESSING THE OTHER SIDE OF THE PLATE TO DEFORM IT INTO ENGAGEMENT WITH SAID TOP, AND THEREAFTER WHILE CONTINUING TO HOLD ITS MARGIN SUPPLYING PRESSURE TO THE SIDE OF THE PLATE ON WHICH SAID STOP IS LOCATED TO DEFLECT THE PLATE FROM ITS DEFORMED CONFIGURATION. 